Touch panel and display device including the same

ABSTRACT

A touch screen of a touch panel includes plural detection column wirings and plural detection row wirings that cross the detection column wirings. Dummy column wirings having a similar configuration to that of the detection column wirings are arrayed at further outer sides of outermost detection column wirings out of the plural detection column wirings. Dummy row wirings having a similar configuration to that of the detection row wirings are arrayed at further outer sides of outermost detection row wirings out of the plural detection row wirings.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a touch panel and a display deviceincluding a touch panel.

2. Description of the Background Art

A touch panel that detects a touch of an indicator such as a finger andspecifies positional coordinates of the touch is attracting attention asone of excellent user interface means. Touch panels according to varioussystems such as resistance film systems and electrostatic capacitancesystems are commercialized.

As one of electrostatic capacitance systems, there is a PCT (ProjectedCapacitive Touchscreen) system that can perform touch detection evenwhen a front surface side of a touch screen in which a touch sensor isincorporated is covered with a protection plate like a glass platehaving a thickness of about a few millimeters (refer to JapaneseUnexamined Patent Application Publication No. H09-511086 (1997), p. 7line 19 to p. 8 line 4, p. 8 line 23 to p. 9 line 6, p. 13 lines 4 to12, and see FIGS. 1, 2, and 8, for example). Because this system canhave the protection plate arrayed on the front surface, the system hasan advantage in that the system has excellent robustness, can detect atouch even when an operator is wearing gloves, and has a long lifebecause there is no moving part.

For example, the touch screen of the touch panel using the PCT systemdescribed in Japanese Unexamined Patent Application Publication No.H09-511086 (1997) includes a first-series conductive material pattern (aconductor element) formed on a thin dielectric film and a second-seriesconductive material pattern (a conductor element) formed via aninsulating film, as detection wirings for detecting electrostaticcapacitances. Between the conductor elements, there is no electriccontact, and a plurality of intersections are formed. Materials suitedfor conductive materials are metal materials such as silver, forexample. Visibility becomes a problem in displaying. To reducevisibility, indium tin oxide (ITO) is used. A thin electric wire of 10μm to 20 μm can be also used in place of a conductive material pattern.

A conductor element that detects electrostatic capacitances is connectedto a capacitance control oscillator via an output line and amultiplexer. Outputs of the conductor element are counted by a divider,and are used as capacitance detection data.

In Japanese Patent Application Laid-Open Publication No. 2010-257178 (p.5 lines 10 to 17, FIG. 4) described below, there is proposed a techniquefor providing a dummy drawing wiring at a further outer end of anoutermost leading line, out of a plurality of leading lines that connectbetween a detection wiring and a terminal, on a touch screen of a touchpanel. On the touch panel, a deviation between a parasitic capacitanceof an outermost leading line and a parasitic capacitance of otherleading line is suppressed, by applying a predetermined potential to thedummy drawing wiring. With this arrangement, a deviation of detectionsensitivities of electrostatic capacitances of detection wirings can bereduced.

SUMMARY OF THE INVENTION

According to the touch panels of the electrostatic capacitance systemsas described in Japanese Unexamined Patent Application Publication No.H09-511086 (1997) and in Japanese Patent Application Laid-OpenPublication No. 2010-257178, a relaxation oscillator and a hysteresisoscillator can be used as a capacitance detecting circuit. Anoscillation cycle of a capacitance detecting circuit is generallydetermined by a charge/discharge time constant of a resistor element anda capacitor element. Therefore, by using a part of the capacitanceelement as an electrostatic capacitance (hereinafter, “touchcapacitance”) that is formed between a detection wiring and anindicator, the oscillation cycle of the capacitance detecting circuitchanges according to the touch capacitance. The touch panel of theelectrostatic capacitance system determines presence of a touch and atouch position, by detecting a change of the oscillation cycle. Toobtain satisfactory detection precision of a touch, a parasiticcapacitance and a wiring resistance of a detection wiring need to bedecreased as far as possible.

An area of an electrode formed on the touch panel by the user's fingertouch is generally about one square centimeter and there is littledifference, and a formed touch capacitance is about a few pF, althoughthere is some difference depending on age and a body type of the user.Because there is a spread of an electric field in the touch capacitance,a position of a finger touch between detection wirings can be alsodetected by interpolating between adjacent detection wirings.

However, when an interval between detection wirings becomes larger thana finger width by a constant amount or more (specifically, the intervalalso depends on a distance between an electrode formed by a finger touchand a detection wiring (a thickness of a protection glass)), a change ofan electrostatic capacitance by the finger touch does not appear inadjacent detection wirings. Therefore, position detection by theinterpolation between the detection wirings becomes impossible.Consequently, when detection resolution of a touch position in the touchpanel is set uniform, the interval between the adjacent detectionwirings becomes constant.

In the case of using a touch panel in combination with a display panelof a liquid-crystal display device or the like, a general display paneldoes not have a square shape but has a vertically long or laterally longshape in many case. Therefore, usually, a shape of a detection region ofthe touch panel is also matched with the shape of the display panel. Toobtain satisfactory detection precision of a touch, it is desirable thata parasitic capacitance formed between each detection wiring of thetouch screen and the display panel is set as uniform as possible.

When a touch panel is combined with a display panel, there is a risk ofreduction in detection precision of a touch, particularly in thedetection wirings that are arrayed at peripheral portions of a touchscreen, due to noise generated in the display panel. Although dependingon a distance between the display panel and the detection wirings,parasitic capacitances increase due to sneak capacitance and the like ata periphery, on the detection wirings arrayed at peripheral portions ofthe touch panel. A difference occurs between these parasiticcapacitances and parasitic capacitances of other detection wirings. Whenparasitic capacitances vary in detection wirings, there arises a problemin that detection sensitivities of the touch screen become non-uniform,and a normal touch detection cannot be performed at near an end portionof the touch panel.

A technique of Japanese Patent Application Laid-Open Publication No.2010-257178 sets parasitic capacitances of drawing wirings uniform, butcannot suppress variations of parasitic capacitances of detectionwirings, and does not solve the above problems.

An object of the present invention is to suppress variations ofparasitic capacitances of detection wirings on a touch panel thatincludes a plurality of detection wirings.

A touch panel according to the present invention includes a touch screenthat includes a plurality of detection wirings arrayed in parallel, andparasitic capacitance setting means that sets parasitic capacitances ofan outermost detection wiring out of the plurality of detection wiringsequal to parasitic capacitances of other detection wirings.

Because parasitic capacitances of a plurality of detection wirings areset uniform, variations of detection sensitivities of a touch on thetouch screen can be suppressed. Accordingly, an effect of improvement ofdetection precision of a touch can be obtained.

These and other objects, features, aspects and advantages of the presentinvention will become more apparent from the following detaileddescription of the present invention when taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view showing a configuration of a touch screen of atouch panel according to a first preferred embodiment;

FIG. 2 is a partial plan view showing a configuration of detectioncolumn wirings and detection row wirings of the touch panel according tothe first preferred embodiment;

FIG. 3 is a cross-sectional view showing a cross-sectional configurationof the touch screen in the touch panel according to the first preferredembodiment;

FIG. 4 is a view showing a total configuration of the touch panelaccording to the first preferred embodiment;

FIG. 5 is a view showing a configuration of a detecting circuit includedin the touch panel according to the first preferred embodiment;

FIG. 6 is a view showing a configuration of an oscillation circuitincluded in a detection oscillation circuit of the touch panel accordingto the first embodiment;

FIG. 7 is a view showing a configuration of a detection oscillationcircuit of a conventional touch panel;

FIG. 8 is an explanatory view of a parasitic capacitance added todetection row wirings of the conventional touch panel;

FIG. 9 is a view showing a distribution of detection sensitivities ofdetection row wirings of the conventional touch panel;

FIG. 10 is a view showing a configuration of a detection oscillationcircuit of the touch panel according to the first preferred embodiment;

FIG. 11 is an explanatory view of a parasitic capacitance added todetection row wirings of the touch panel according to the firstpreferred embodiment;

FIG. 12 is a view showing a distribution of detection sensitivities ofdetection row wirings of the touch panel according to the firstpreferred embodiment;

FIG. 13 is a view showing a configuration of a detection oscillationcircuit of a touch panel according to a second preferred embodiment; and

FIG. 14 is an explanatory view of a parasitic capacitance added todetection row wirings of the touch panel according to the secondpreferred embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS First Preferred Embodiment

FIG. 1 is a plan view schematically showing a configuration of a touchscreen 1 of a touch panel according to the present invention. As shownin FIG. 1, the touch screen 1 includes a plurality of detection columnwirings 2 that are extended to a column direction (a y direction shownin FIG. 1) and are arrayed in parallel at a predetermined pitch, and aplurality of detection row wirings 3 that are extended to a rowdirection (an x direction shown in FIG. 1) and are arrayed in parallelat a predetermined pitch. Further, near an end portion on the touchscreen 1, there is arrayed a terminal group 8 that includes a pluralityof terminals 2 a connected to the detection column wirings 2 via leadinglines, and a plurality of terminals 3 a connected to the detection rowwirings 3 via leading lines.

The touch panel detects a position of an indicator such as a finger of auser on the touch screen 1, by detecting an electrostatic capacitance (atouch capacitance) formed between the indicator and the detection columnwiring 2 and the detection row wiring 3 when the indicator touches thetouch screen 1, by using a detecting circuit (not shown in FIG. 1)connected to the terminal group 8.

FIG. 2 is a partially enlarged plan view of the detection column wirings2 and the detection row wirings 3. The detection column wirings 2 andthe detection row wirings 3 are wiring groups, each group including abundle of a plurality of thin lines 2 b, 3 b, respectively. In otherwords, each group of the detection column wirings 2 and the detectionrow wirings 3 has a plurality of slit opening portions that are extendedto a longitudinal direction.

When each of the detection column wirings 2 and the detection rowwirings 3 is what is called a “solid wiring” that does not have anopening portion, for example, a touch capacitance formed by theindicator can be set large. However, when the touch screen 1 is arrayedon a front surface of the display panel, the detection column wirings 2and the detection row wirings 3 interrupt transmission of a displaybeam. Therefore, this lowers brightness of a screen of the displaypanel. When the slit opening portions are formed on the detection columnwirings 2 and the detection row wirings 3 as shown in FIG. 2, openingareas of the touch screen 1 becomes large, and therefore, reduction ofbrightness of the screen can be suppressed.

In the present preferred embodiment, it is assumed that the touch panelis arrayed on the front surface of the display panel such as aliquid-crystal display panel, and that the detection column wirings 2and the detection row wirings 3 are wiring groups, each group includinga bundle of the plurality of thin lines 2 b, 3 b, respectively. Thetouch panel according to the present invention can be combined with allkinds of display panels of display devices such as an organic EL(electro-luminescence) display panel and a PDP (Plasma Display Panel),for example, without being limited to a liquid-crystal display panel.

More specifically, it is desirable that the detection column wirings 2and the detection row wirings 3 are formed of a metal such as Cu and Al,for example, and that widths of the thin lines 2 b, 3 b are equal to orsmaller than 20 μm to obtain satisfactory visibility of a displayscreen. Numbers, widths, and pitches of the thin lines 2 b of thedetection column wirings 2 and the thin lines 3 b of the detection rowwirings 3, respectively, and numbers, widths, and pitches of thedetection column wirings 2 and the detection row wirings 3, respectivelyare suitably selected corresponding to resolutions that are required todetect a size of the touch screen 1 and a touch position (touchcoordinates).

A light transmission rate of the touch screen 1 can be set high, evenwhen the detection column wirings 2 and the detection row wirings 3 areformed of a transparent wiring material (a conductive material) such asITO. However, because a sheet resistance value of ITO is relativelyhigh, even when the detection column wirings 2 and the detection rowwirings 3 of ITO are solid wirings, a resistance of ITO cannot bedisregarded when a touch panel size becomes large, and therefore, adetection sensitivity of a touch capacitance becomes low. Accordingly,it is preferable that the detection column wirings 2 and the detectionrow wirings 3 have a structure made of the thin lines 2 b, 3 b of ametal.

On the touch screen 1 of the present preferred embodiment, there arearrayed dummy column wirings 4 of the same structure (the same shape andthe same width) as that of the detection column wirings 2, such that thedummy column wirings 4 are adjacent in parallel to further outer sidesof the outermost (both ends) detection column wirings 2, as shown inFIG. 1. Similarly, dummy row wirings 5 are arrayed such that the dummyrow wirings 5 are adjacent in parallel to further outer sides of theoutermost detection row wirings 3. Operation and effects of the dummycolumn wirings 4 and the dummy row wirings 5 are described later.

FIG. 3 is a view showing a cross-sectional structure of the touch screen1, and shows a part of a cross section along line A1-A2 in FIG. 1. Asshown in FIG. 3, the touch screen 1 has a transparent substrate 9(hereinafter, “base substrate”) made of transparent glass or resin, as abase material. The detection column wirings 2 are arrayed on the basesubstrate 9. A top of the detection column wirings 2 is covered with atransparent interlayer insulating film 10 such as a silicon oxide (SiO₂)film and a silicon nitride (SiN) film. The detection row wirings 3 areformed on the interlayer insulating film 10.

A top of the detection row wirings 3 is covered with a protection film11 as a transparent insulation film similar to the interlayer insulatingfilm 10. The leading lines and the terminals 2 a that are connected tothe detection column wirings 2 are formed by using the same wiring layeras that of the detection column wirings 2. The leading lines and theterminals 3 a that are connected to the detection row wirings 3 areformed by using the same wiring layer as that of the detection rowwirings 3. As shown in FIG. 3, contact holes to which upper surfaces ofthe terminals 2 a, 3 a are exposed are formed on the interlayerinsulating film 10 and the protection film 11.

When the touch screen 1 is arrayed on the front surface of the displaypanel like in the present preferred embodiment, a transparent dielectricfilm 12 like ITO is formed on a lower surface of the base substrate 9,to prevent the touch screen 1 from receiving an influence of noise fromthe display panel. When the influence of noise from the display panelcan be disregarded, the dielectric film 12 may be omitted.

FIG. 4 is a view showing a total configuration of the touch panelaccording to a first preferred embodiment. FIG. 4 shows a state that acontroller substrate 14 on which a detecting circuit 15 of a touchcapacitance is mounted is connected to the touch screen 1. Each terminalof an FPC 13 (Flexible Printed Circuit) is mounted on the terminal group8 of the touch screen 1, by using an ACF (Anisotropic Conductive Film)or the like. The terminal group 8 is connected to the detecting circuit15 on the controller substrate 14 via the FPC 13.

The detecting circuit 15 is for detecting a touch capacitance formedbetween the indicator such as a finger and the detection column wiring 2and the detection row wiring 3, detecting a touch by the indicator, andcalculating touch coordinates. Touch coordinate data that are calculatedby the detecting circuit 15 are inputted to an external computer (notshown) or the like.

FIG. 5 is a view showing a configuration of the detecting circuit 15included in the touch panel according to the present preferredembodiment. In this case, FIG. 5 shows an example that the touch panelincludes eight series (eight) of the detection column wirings 2 and thedetection row wirings 3, respectively. That is, the touch panel includesdetection column wirings Wc1 to Wc8 as the detection column wirings 2,and includes detection row wirings Wr1 to Wr8 as the detection rowwirings 3. Further, the touch panel includes a dummy column wiring Wcd1that is arrayed at an outer side of the detection column wiring Wc1, anda dummy column wiring Wcd2 that is arrayed at an outer side of thedetection column wiring Wc8, as the dummy column wirings 4, and includesa dummy row wiring Wrd1 that is arrayed at an outer side of thedetection row wiring Wr1, and a dummy row wiring Wrd2 that is arrayed atan outer side of the detection row wiring Wr8, as the dummy row wirings5.

The detecting circuit 15 is configured by a column-wiring selectionswitch circuit 20 a, a row-wiring selection switch circuit 20 b, anoscillation circuit 21, a first counting circuit 23 a, a second countingcircuit 23 b, a touch-coordinate calculating circuit 24, and a controlcircuit 25.

The column-wiring selection switch circuit 20 a includes at one endswitches RLc1 to RLc8 that are connected to the detection column wiringsWc1 to Wc8, respectively, and the row-wiring selection switch circuit 20b includes at one end switches RLw1 to RLw8 that are connected to thedetection row wirings Wr1 to Wr8, respectively.

The other ends of the switches RLc1 to RLc8 and the switches RLw1 toRLw8 are all connected to a node N3 as an input terminal of theoscillation circuit 21. The column-wiring selection switch circuit 20 a(the switches RLc1 to RLc8) and the row-wiring selection switch circuit20 b (the switches RLw1 to RLw8) change over the detection columnwirings 2 and the detection row wirings 3 to be connected to theoscillation circuit 21, by each predetermined number in a predeterminedorder, and scan, following an instruction (a REPLAY control) from thecontrol circuit 25.

Oscillation signals that are outputted from the oscillation circuit 21are inputted to a counting unit which includes the first countingcircuit 23 a and the second counting circuit 23 b. Upon receiving areset signal from the control circuit 25, the first counting circuit 23a resets a count value. Upon receiving a subsequent enable signal, thefirst counting circuit 23 a counts the oscillation signals from theoscillation circuit 21 until when the count value reaches apredetermined value. The second counting circuit 23 b resets the countvalue upon receiving a reset signal. Upon receiving an enable signal,the second counting circuit 23 b counts clock signals until when thecount value of the first counting circuit 23 a becomes the abovepredetermined value.

That is, the second counting circuit 23 b counts time from when thefirst counting circuit 23 a starts counting oscillation signals of theoscillation circuit 21 until when the count value reaches thepredetermined value. Therefore, the count value of the second countingcircuit 23 b is proportional to a cycle of oscillation signals of theoscillation circuit 21, and an oscillation cycle of the oscillationcircuit 21 is known from a count value of the second counting circuit 23b.

The count value (corresponding to the oscillation cycle of theoscillation circuit 21) of the second counting circuit 23 b is inputtedto the touch-coordinate calculating circuit 24. As described later, theoscillation cycle of the oscillation circuit 21 is generally determinedby a charge/discharge time constant decided by a resistance and acapacitance connected to the node N3. Because the detection columnwirings Wc1 to Wc8 and the detection row wirings Wr1 to Wr8 aresequentially connected to the node N3 via the column-wiring selectionswitch circuit 20 a and the row-wiring selection switch circuit 20 b,when the indicator such as a finger touches the touch screen 1 and whena touch capacitance is formed between any one of the detection columnwirings Wc1 to Wc8 and any one of the detection row wirings Wr1 to Wr8,the oscillation cycle of the oscillation circuit 21 changes at a timingcorresponding to this position.

The touch-coordinate calculating circuit 24 holds the oscillation cycleof the oscillation circuit 21 obtained from a coefficient value of thesecond counting circuit 23 b, in an inside storage unit. Thetouch-coordinate calculating circuit 24 detects a change of theoscillation cycle at a last scanning time of the detection columnwirings Wc1 to Wc8 and the detection row wirings Wr1 to Wr8, and achange of the oscillation cycle within a scanning of the same scanningtime, and calculates positional coordinates (touch coordinates) of theindicator based on the detection.

In this way, in the touch panel according to the present preferredembodiment, the detection column wirings 2 (Wc1 to Wc8) and thedetection row wirings 3 (Wr1 to Wr8), the column-wiring selection switchcircuit 20 a, the row-wiring selection switch circuit 20 b, and theoscillation circuit 21 constitute a detection oscillation circuit 22that generates an oscillation signal corresponding to touch coordinates.The touch-coordinate calculating circuit 24 calculates touch coordinatesbased on the oscillation cycle of the detection oscillation circuit 22.

The oscillation cycle of the detection oscillation circuit 22 isdescribed. FIG. 6 is a view showing a configuration of the oscillationcircuit 21 included in the detection oscillation circuit 22. Anoperation principle of the detection oscillation circuit 22 is describedbelow with reference to FIG. 6.

To simplify the description, the detection oscillation circuit 22 isassumed to be configured by the detection row wirings 3 (Wr1 to Wr8),the row-wiring selection switch circuit 20 b, and the oscillationcircuit 21. The description is performed by omitting the detectioncolumn wirings 2 and the column-wiring selection switch circuit 20 a.The dummy column wirings 4 (Wcd1, Wcd2) and the dummy row wirings 5(Wrd1, Wrd2) are also omitted from FIG. 6.

The oscillation circuit 21 is configured by using an operation amplifier30. A resistor element Ra is connected between a non-inverting inputterminal of the operation amplifier 30 and a ground. A resistor elementRb is connected between the non-inverting input terminal of theoperation amplifier 30 and an output terminal. A capacitor element C1 isconnected between the non-inverting input terminal of the operationamplifier 30 and the ground. A resistor element R1 is connected betweenthe non-inverting input terminal of the operation amplifier 30 and anoutput terminal.

The oscillation circuit 21 shown in FIG. 6 is what is called arelaxation oscillation circuit. The oscillation circuit 21 oscillatesbased on a charge/discharge performed by a feedback circuit 32(hereinafter, “detection feedback path”) which is configured byelectrostatic capacitances of the detection row wirings Wr1 to Wr8 and atouch capacitor Ct in addition to the resistor element R1 and thecapacitor element C1, from positive and negative output saturationvoltages. Oscillation signals are outputted from the output terminal ofthe operation amplifier 30.

An oscillation cycle Tc of the oscillation circuit 21 as a single unitthat does not include the detection row wirings 3 and the row-wiringselection switch circuit 20 b becomes generally as shown by Equation (1)below, and is proportional to a time constant τ of a feedback path whichincludes the resistor element R1 and the capacitor element C1.

Tc=2τ·ln((1+k)/(1−k))  (1)

In Equation (1), τ=R1·C1, and k=Ra/(Ra+Rb). Further, R1, C1, Ra, Rb thatare used in Equation (1) designate resistance values of resistorelements and an electrostatic capacitance value of a capacitor element.

Therefore, in the detection oscillation circuit 22 that also includesthe detection row wirings 3 and the row-wiring selection switch circuit20 b, when the touch capacitor Ct is formed near an indicator 33 such asa finger and any one of the detection row wirings Wr1 to Wr8 by a touchof the indicator, a time constant τ increases due to the detectionfeedback path 32, and the oscillation cycle of the detection oscillationcircuit 22 becomes large. As described earlier, in the touch panelaccording to the present preferred embodiment, touch coordinates aredetected by detecting a change of the oscillation cycle of the detectionoscillation circuit 22, by using the first counting circuit 23 a and thesecond counting circuit 23 b shown in FIG. 5.

However, as described later, because resistor components of thedetection row wirings Wr1 to Wr8 enter in series with the touchcapacitor Ct, when resistance values of the detection row wirings Wr1 toWr8 are large, a degree of increase in the oscillation cycle due tooccurrence of the touch capacitor Ct becomes small, and detectionsensitivity of the touch capacitor Ct becomes low. Further, a parasiticcapacitance is added between the detection column wirings 2 (not shownin FIG. 6) and the display panel, in each of the detection row wiringsWr1 to Wr8. A detection sensitivity of the touch capacitor Ct alsobecomes low when the parasitic capacitance is large.

In the above calculation of the oscillation cycle, to simplify thedescription, parasitic capacitances following the detection columnwirings 2, the detection row wirings 3, the leading lines that connectbetween these wirings and the terminal group 8, and other wirings, andelectrostatic capacitances observed from input/output terminals of thecolumn-wiring selection switch circuit 20 a and the row-wiring selectionswitch circuit 20 b (that is, electrostatic capacitances inside thecolumn-wiring selection switch circuit 20 a and the row-wiring selectionswitch circuit 20 b) are not taken into account. Actually, it isnecessary to select parameters of each circuit such as a resistancevalue, after taking these electrostatic capacitances into account.However, because these electrostatic capacitances do not affect theessence of the present preferred embodiment, the description isperformed by omitting these electrostatic capacitances.

A parasitic capacitance that is added to the detection row wirings 3 orthe detection column wirings 2 (not shown) of the touch screen 1 isdescribed. FIG. 7 shows a configuration of the detection oscillationcircuit 22 included in a conventional touch panel. Although theconventional detection oscillation circuit 22 also actually has thedetection column wirings 2 and the column-wiring selection switchcircuit 20 a, the detection column wirings 2 and the row-wiringselection switch circuit 20 b are omitted from the drawing, to simplifythe description. The conventional touch panel does not have the dummycolumn wirings 4 (Wcd1, Wcd2) and the dummy row wirings 5 (Wrd1, Wrd2),and it does not mean that these dummy column wirings and dummy rowwirings are omitted from FIG. 7. It is desirable that wiring resistancevalues (Rr) of the detection row wirings 3 are all equal, and similarlyit is desirable that the wiring resistance values of the detectioncolumn wirings 2 (not shown) are all equal.

FIG. 8 is a view showing a part of a cross section along line B1-B2 inFIG. 7, and corresponds to a portion near three detection row wirings(Wr6 to Wr8) at an end out of eight detection row wirings Wr1 to Wr8.The transparent dielectric film 12 like ITO is formed on a lower surfaceof the base substrate 9, to prevent the touch panel from receiving aninfluence of noise from the display panel.

As shown in FIG. 8, a parasitic capacitance Cstr2 formed between each ofthe detection row wirings Wr1 to Wr8 and the dielectric film 12 belowthese wirings is added to each detection row wiring. In addition to theparasitic capacitance Cstr2, a parasitic capacitance Cstr3 is added toeach of the detection row wirings Wr1, Wr8 that are arrayed at bothends, due to the influence of sneak capacitance at a periphery.Therefore, a parasitic capacitance Cstr1 (FIG. 7) that is added to thedetection row wirings Wr1, Wr8 at both ends becomes Cstr2+Cstr3, and theparasitic capacitance of other detection row wirings Wr2 to Wr7 becomesCstr2. As a result, a difference occurs between these parasiticcapacitances.

In this case, there arises a difference between a detection sensitivityof a touch at a position near the detection row wirings Wr1, Wr8 at bothends and a detection sensitivity of a touch at a position near thedetection row wirings Wr2 to Wr7. As a result, detection precision of atouch capacitance on the touch screen 1 is aggravated. Even when thedielectric film 12 is not formed on the lower surface of the basesubstrate 9, there arises a difference between the parasitic capacitanceof the detection row wirings Wr1, Wr8 at both ends and the parasiticcapacitance of the other detection row wirings Wr2 to Wr7, by receivingan influence of the display panel and the like.

FIG. 9 is a view showing an example of measurement values of touchdetection sensitivities of the detection row wirings 3 on theconventional touch panel (having no dummy row wirings 5) that has 21detection row wirings 3. In FIG. 9, an X axis represents row numbers ofthe detection row wirings 3, and a Y axis represents detectionsensitivities (normalized by setting a highest value as 1). It isunderstood from FIG. 9 that detection sensitivities of the detection rowwirings 3 at both ends (a first row and a twenty-first row) are lowerthan other detection sensitivities.

A main reason for this is considered that, as described above, theparasitic capacitances of the detection row wirings 3 at both ends arehigher than the parasitic capacitances of the other detection rowwirings 3. Therefore, to equalize the detection sensitivities of all thedetection row wirings 3, it is valid to equalize the parasiticcapacitances of all the detection row wirings 3.

FIG. 10 is a view showing a configuration of the detection oscillationcircuit 22 included in the touch panel according to the first preferredembodiment. In the detection oscillation circuit 22, the dummy rowwirings Wrd1, Wrd2 of a configuration similar (a shape and a width arethe same) to that of the detection row wirings Wr1 to Wr8 are arrayed atfurther outer sides of the detection row wirings Wr1, Wr8 that arearrayed at both ends, out of the detection row wirings 3 (Wr1 to Wr8),at an interval similar to the interval of the detection row wirings Wr1to Wr8.

The detection oscillation circuit 22 according to the present preferredembodiment actually also has the detection column wirings 2 (Wc1 to Wc8)and the column-wiring selection switch circuit 20 a, as shown in FIG. 5.Further, the dummy column wirings 4 (Wcd1, Wcd2) of a configurationsimilar to that of the detection column wirings 2 are arrayed at furtherouter sides of the detection column wirings 2 (Wc1, Wc8) at both ends,at an interval similar to the interval of the detection column wiringsWc1 to Wc8. However, these detection column wirings are omitted from thedrawing to simplify the description. It is desirable that the wiringresistance values (Rr) of the detection row wirings 3 are all equal, andthis is similarly applied to the detection column wirings 2 (not shown).

FIG. 11 is a view showing a part of a cross section along line B1-B2 inFIG. 10, and corresponds to three detection row wirings (Wr6 to Wr8) atan end out of eight detection row wirings Wr1 to Wr8, and a portion nearthe dummy row wiring Wrd2 arrayed at an outer side of the threedetection row wirings. The transparent dielectric film 12 like ITO isalso formed on a lower surface of the base substrate 9, to prevent thetouch panel from receiving an influence of noise from the display panel.

As shown in FIG. 11, the parasitic capacitance Cstr2 formed between eachof the detection row wirings Wr1 to Wr8 and the dielectric film 12 belowthese wirings is added to each detection row wiring. Unlike in theconventional structure (FIG. 8), the parasitic capacitance Cstr3 due tothe influence of sneak capacitance at a periphery is not added to thedetection row wirings Wr1, Wr8. On the other hand, the parasiticcapacitance Cstr3 due to the influence of sneak capacitance at aperiphery is added, in addition to the parasitic capacitance Cstr2, tothe dummy row wirings Wrd1, Wrd2 arrayed at outer sides of the detectionrow wirings Wr1, Wr8, like the detection row wirings Wr1, Wr8 in theconventional structure (FIG. 8).

In this way, the detection row wirings Wr1, Wr8 are set in anenvironment substantially similar to that of the other detection rowwirings Wr2 to Wr7, by arraying the dummy row wirings Wrd1, Wrd2 atfurther outer sides of the detection row wirings Wr1, Wr8 at both ends.Therefore, the parasitic capacitance Cstr3 due to the influence of sneakcapacitance at a periphery is not added to the detection row wiringsWr1, Wr8. As a result, the parasitic capacitances of all the detectionrow wirings Wr1 to Wr8 become uniform. Consequently, variations ofdetection sensitivities of touch capacitances in a column direction aresuppressed, and an effect of improvement of detection precision of atouch is obtained.

The dummy column wirings 4 (Wcd1, Wcd2) arrayed at outer sides of thedetection column wirings 2 (Wc1 to Wc8) also have an effect similar tothe above effect, although the description of this is omitted here. Thatis, by arraying the dummy column wirings 4 (Wcd1, Wcd2) at further outersides of the detection column wirings 2 (Wc1, Wc8) at both ends,parasitic capacitances due to the influence of sneak capacitance at aperiphery are not added to the detection column wirings 2 (Wc1, Wc8) atboth ends. As a result, parasitic capacitances become uniform for allthe detection column wirings 2. Consequently, variations of detectionsensitivities of touch capacitances in a row direction can besuppressed, and detection precision of the touch capacitances improves.

FIG. 12 is a view showing an example of measurement values of touchdetection sensitivities of the detection row wirings 3 on the touchpanel that has 21 detection row wirings 3 according to the presentinvention. In FIG. 12, the measurement values according to aconventional technique shown in FIG. 9 are also plotted for comparison.As shown in FIG. 12, in the present invention, detection sensitivitiesof the detection row wirings 3 at both ends (a first row and atwenty-first row) are higher than those according to the conventionaltechnique, and are values near values of other detection sensitivities.A reason for this is that the parasitic capacitances of the detectionrow wirings 3 at both ends are not easily affected by sneak capacitanceat a periphery and become values near values of the parasiticcapacitances of the other detection row wirings 3.

In the present preferred embodiment, although the dummy row wirings 5are arrayed at both outer sides of the detection row wirings 3, thedummy row wiring 5 may be arranged to be arrayed at only one outer side.In this case, the above effect is obtained in the detection row wiring 3at a side where the dummy row wiring 5 is arrayed. This is alsosimilarly applied to the dummy column wirings 4 that are arrayed atouter sides of the detection column wirings 2.

In the present preferred embodiment, although one dummy row wiring 5 isarrayed at each outer side of the detection row wirings 3, the pluralityof dummy row wirings 5 may be arranged to be arrayed at each outer sideof the detection row wirings 3. With this arrangement, an effect ofpreventing the detection row wirings 3 from receiving an influence ofsneak capacitance at a periphery further improves. This is alsosimilarly applied to the dummy column wirings 4 that are arrayed atouter sides of the detection column wirings 2.

A structure (a shape and a width) of the dummy row wiring 5 ispreferably the same as a structure of each of the detection row wirings3. An interval between the dummy row wiring 5 and an outermost detectionrow wiring 3 is preferably the same as an interval between the detectionrow wirings 3. With this arrangement, the outermost detection rowwirings 3 and the other detection row wirings 3 are set in a more equalenvironment, and the parasitic capacitances of the detection row wirings3 become more uniform. When the detection row wirings 3 include theplurality of thin lines 3 b as shown in FIG. 2, for example, the dummyrow wirings 5 are also preferably in a similar configuration. However, astructure and an interval of the dummy row wirings 5 are not limited tothe above, and may be a structure and an interval that are differentfrom those of the detection row wirings 3, within a range in which theeffect of the present invention is obtained.

Also, for the dummy column wirings 4, a structure is preferably the sameas that of the detection column wirings 2, and an interval between thedummy column wiring 4 and an outermost detection column wiring 2 is thesame as the interval between the detection column wirings 2. However, astructure and an interval of the dummy row wirings 4 are not limited tothe above, and may be a structure and an interval that are differentfrom those of the detection row wirings 2, within a range in which theeffect of the present invention is obtained.

A method for manufacturing a touch panel according to the presentpreferred embodiment is described next with reference to FIG. 3. First,on the base substrate 9 made of glass, a metal having aluminum as a maincomponent, such as an Al alloy including Ni, AlNiNd, for example, isformed by a sputtering method, as a first conductive thin film thatbecomes the detection column wirings 2, the dummy column wirings 4, theterminals 2 a, and the leading lines of the terminals. A film-formingcondition to be applied is that a pressure is 0.2 Pa to 0.5 Pa, DC poweris 1.0 kW to 2.5 kW, that is, 0.17 W/cm² to 0.43 W/cm² as power density,and a film-forming temperature is within a range from a room temperatureto about 180° C. The first conductive thin film is formed in a thicknessof 150 nm to 500 nm.

To suppress a reaction with a developing solution, a nitrided AlNiNdNlayer may be formed on an AlNiNd layer of the first conductive thinfilm. AlNiSl or AlNiMg may be used instead of the AlNiNd. Alternatively,the first conductive thin film may be made of the same material as thatof a second conductive thin film that becomes the detection row wirings3, the dummy row wirings 5, the terminals 3 a, and the leading lines ofthe terminals, that are formed afterward. With this arrangement,production efficiency improves. Cu or a Cu alloy other than Al can bealso used as a low-resistance metal material. In this case, the film canbe also formed by the sputtering method in a similar manner to that ofAl.

Next, a resist that has shapes of the detection column wirings 2, thedummy column wirings 4, the terminals 2 a, and the leading lines of theterminals is formed on the first conductive thin film, by aphotolithography technique. Next, by using the resist as a mask, thedetection column wirings 2, the dummy column wirings 4, the terminals 2a, and the leading lines are formed, by patterning the first conductivethin film, by etching using a mixed acid of phosphoric acid, nitricacid, and acetic acid, for example. When a cross-sectional shape of thedetection column wirings 2, the dummy column wirings 4, the terminals 2a, and the leading lines of the terminals is formed in a tapered shape,coverage of the interlayer insulating film 10 that is formed on theseitems improves. With this arrangement, a defect such as a disconnectionof an upper wiring layer can be prevented. Although etching using amixed acid of phosphoric acid, nitric acid, and acetic acid is usedabove, a kind of an etching solution is not limited to this. Dry etchingmay be also used.

Next, the interlayer insulating film 10 is formed to cover the detectioncolumn wirings 2, the dummy column wirings 4, the terminals 2 a, and theleading lines of the terminals, by a method like plasma CVD. A siliconoxide (SiO₂) film of a low dielectric rate is used as the interlayerinsulating film 10. A film-forming condition of the silicon oxide filmused is that a flow rate of SiH₄ is 10 sccm to 50 sccm, a flow rate ofN₂O is 200 sccm to 500 sccm, a film-forming pressure is 50 Pa, RF poweris 50 W to 200 W, that is, 0.015 W/cm² to 0.67 W/cm², and a film-formingtemperature is 200° C. to 300° C.

It is desirable that a film thickness of the interlayer insulating film10 is as large as possible, to reduce parasitic capacitances that areformed between the detection column wirings 2 and the detection rowwirings 3. The film thickness may be determined by taking productionefficiency into account. The interlayer insulating film 10 is notlimited to a SiO₂ film, and may be a SiN film or a SiON film. In thiscase, the interlayer insulating film 10 is formed by adding hydrogen,nitrogen, and NH₃ to a material gas of a SiO₂ film.

After the interlayer insulating film 10 is formed, as the secondconductive thin film that becomes the detection row wirings 3, the dummyrow wirings 5, the terminals 3 a, and the leading lines of theterminals, there is formed a metal having aluminum as a main component,such as an Al alloy including Ni, AlNiNd, for example, by the sputteringmethod. A film-forming condition is that a pressure is 0.2 Pa to 0.5 Pa,DC power is 1.0 kW to 2.5 kW, that is, 0.17 W/cm² to 0.43 W/cm² as powerdensity, and a film-forming temperature is within a range from a roomtemperature to about 180° C. The second conductive thin film is formedin a thickness of 200 nm to 1000 nm.

To suppress a reaction with a developing solution, a nitrided AlNiNdNlayer may be formed on AlNiNd of the second conductive thin film.AlNiSl, AlNiMg or the like may be used instead of the AlNiNd. Cu or a Cualloy other than Al can be also used as a low-resistance metal material.In this case, the film can be also formed by the sputtering method in asimilar manner to that of Al.

It is desirable that a film thickness of the second conductive thin filmis as large as possible. However, a loss amount and size variations ofCD (Critical Dimension) that occur in a subsequent etching process tendto become larger when a film thickness of the second conductive thinfilm becomes larger. When the film thickness is large, productivity isalso aggravated. Therefore, the thickness of the second conductive thinfilm is set at a proper film thickness within a range in whichvariations of detection sensitivities of a touch can be suppressed asfar as possible.

Next, there is formed a resist that has shapes of the detection rowwirings 3, the dummy row wirings 5, the terminals 3 a, and the leadinglines of the terminals, by the photolithography technique. Next, byusing the resist as a mask, the detection row wirings 3, the dummy rowwirings 5, the terminals 3 a, and the leading lines of the terminals areformed, by patterning the second conductive thin film, by etching usinga mixed acid of phosphoric acid, nitric acid, and acetic acid, forexample. A kind of an etching solution that is used in this etchingprocess is not limited to a mixed acid of phosphoric acid, nitric acid,and acetic acid. Dry etching may be also used.

Next, the protection film 11 is formed to protect the touch panel. Forthe protection film 11, the same kind of a film as that of theinterlayer insulating film 10 is sufficient to obtain satisfactoryvisibility of the screen of the display panel. For example, when theinterlayer insulating film 10 is a silicon oxide (SiO₂) film, theprotection film 11 is formed by the SiO₂ film. A film thickness of theprotection film 11 may be determined by taking coverage and productivityinto account.

Next, by the photolithography technique, a resist that has upperportions of the terminals 2 a, 2 a opened is formed, and the protectionfilm 11 and the interlayer insulating film 10 are patterned by etchingtogether, by etching using a plasma of a mixed gas of CF₄ and O₂, forexample. With this arrangement, contact holes for exposing uppersurfaces of the terminals 2 a, 2 b are formed.

When the touch panel is used in combination with the display panel, thetransparent dielectric film 12 for suppressing reduction of detectionprecision of a touch due to noise from the display panel is formed on alower surface of the base substrate 9, according to a need. As thedielectric film 12, it is preferable to form the film by indium tinoxide (ITO), to prevent reduction of visibility of the display panel,but a film formation is not limited to this method. A thickness of thedielectric film 12 may be determined by taking productivity intoaccount.

In the above process, the touch screen 1 of the configuration shown inFIG. 3 is formed. After this, the touch panel can be obtained byconnecting the controller substrate 14 including the detecting circuit15 to the touch screen 1 via the FPC 13. Further, the display device isassembled by arraying the touch screen 1 of the touch panel on the frontsurface of the display panel.

At the time of arraying the touch panel on the front surface of thedisplay device, a holding mechanism of the touch screen 1 that isconventionally necessary can be eliminated, by directly adhering thetouch screen 1 to the display panel, and the device as a whole can bemade thin. Further, the touch screen 1 and the display panel areintegrated. Therefore, mixing of dusts into a gap between the touchscreen 1 and the display panel in a subsequent process can be prevented,and reduction of visibility of the display panel can be prevented.

Second Preferred Embodiment

In the first preferred embodiment, addition of the parasitic capacitanceCstr3 due to the influence of sneak capacitance at a periphery to thedetection column wirings 2 and the detection row wirings 3 arrayed atthe outermost sides of the detection column wirings 2 and the detectionrow wirings 3 is prevented, by using the dummy column wirings 4 and thedummy row wirings 5. With this arrangement, the parasitic capacitancesof the detection column wirings 2 and the parasitic capacitances of thedetection row wirings 3 are set uniform. In a second preferredembodiment, parasitic capacitances of detection column wirings 2 andparasitic capacitances of detection row wirings 3 are set uniform,without using dummy column wirings 4 and dummy row wirings 5.

FIG. 13 is a view showing a configuration of a detection oscillationcircuit 22 included in a touch panel according to the second preferredembodiment. In the detection oscillation circuit 22, out of detectionrow wirings 3 (Wr1 to Wr8), widths of detection row wirings Wr1, Wr8that are arrayed at outermost sides (both ends) are set smaller thanwidths of other detection row wirings Wr2 to Wr7.

The detection oscillation circuit 22 according to the present preferredembodiment also has detection column wirings 2 (Wc1 to Wc8) and acolumn-wiring selection switch circuit 20 a actually as shown in FIG. 5.However, the detection column wirings and the row-wiring selectionswitch circuit are omitted from the drawing to simplify the description.

FIG. 14 is a view showing a part of a cross section along line B1-B2 inFIG. 13, and corresponds to a portion near three detection row wirings(Wr6 to Wr8) at an end out of eight detection row wirings Wr1 to Wr8.Also in this case, it is assumed that a transparent dielectric film 12like ITO is formed on a lower surface of a base substrate 9, to preventthe touch panel from receiving an influence of noise from the displaypanel.

As shown in FIG. 14, a parasitic capacitance Cstr2 formed between eachof the detection row wirings Wr1 to Wr8 and the dielectric film 12 belowthese wirings is added to each detection row wiring. Like in theconventional structure (FIG. 8), a parasitic capacitance Cstr3 due tothe influence of sneak capacitance at a periphery is added, in additionto a parasitic capacitance Cstr2, to the detection row wirings Wr1, Wr8at both ends.

However, in the present preferred embodiment, because the widths of thedetection row wirings Wr1, Wr8 are smaller than the widths of otherdetection row wirings Wr2 to Wr7, the parasitic capacitance Cstr2between the detection row wirings Wr1, Wr8 and the dielectric film 12becomes smaller than the parasitic capacitance Cstr2 between the otherdetection row wirings Wr2 to Wr7 and the dielectric film 12. When theparasitic capacitance Cstr2 between the detection row wirings Wr1, Wr8and the dielectric film 12 is expressed as “Cstr21”, a parasiticcapacitance Cstr1 (FIG. 13) that is added to the detection row wiringsWr1, Wr8 becomes Cstr21+Cstr3, and a parasitic capacitance that is addedto the other detection row wirings Wr2 to Wr7 becomes Cstr2.

In the present preferred embodiment, widths of the detection row wiringsWr1, Wr8 are set such that the parasitic capacitance Cstr1(Cstr21+Cstr3) of the detection row wirings Wr1, Wr8 becomes equal tothe parasitic capacitance Cstr2 of the other detection row wirings Wr2to Wr7. As a result, the parasitic capacitances become uniform for allthe detection row wirings Wr1 to Wr8. Consequently, variations ofdetection sensitivities of touch capacitances in a column direction canbe suppressed, and an effect of improvement of detection precision ofthe touch is obtained.

For detection column wirings 2 (Wc1 to Wc8), parasitic capacitances canbe also set uniform for all the detection wirings 2, by setting widthsof detection column wirings 2 (Wc1, Wc8) at both ends smaller thanwidths of other detection column wirings 2 (Wc2 to Wc7), although thedescription of this is omitted here. With this arrangement, variationsof detection sensitivities of touch capacitances in a row direction canbe suppressed, and detection precision of the touch capacitancesimproves.

In the present preferred embodiment, although the widths of thedetection row wirings 3 at both ends are set small, a width of thedetection row wiring 3 at only one end can be also set small. In thiscase, the above effect is obtained for the detection row wiring 3 havingthe small width. This is also similarly applied to the detection rowwirings 2.

In the present invention, the preferred embodiments may be freelycombined, or the preferred embodiments may be suitably modified oromitted, within a range of the present invention.

While the present invention has been shown and described in detail, theforegoing description is in all aspects illustrative and notrestrictive. It is, therefore, understood that numerous modificationsand variations can be devised without departing from the scope of theinvention.

What is claimed is:
 1. A touch panel comprising: a touch screenincluding a plurality of detection wirings arrayed in parallel; andparasitic capacitance setting means that sets parasitic capacitances ofan outermost detection wiring out of said plurality of detection wiringsequivalent to parasitic capacitances of other detection wirings.
 2. Thetouch panel according to claim 1, wherein said parasitic capacitancesetting means includes one or more dummy wirings arrayed at furtherouter side of said outermost detection wiring, in parallel with saidoutermost detection wirings
 3. The touch panel according to claim 2,wherein shapes and widths of said dummy wirings are the same as those ofsaid plurality of detection wirings, and an interval between one of saiddummy wirings and said outermost detection wiring is the same as aninterval between said plurality of detection wirings.
 4. The touch panelaccording to claim 2, wherein a plurality of said dummy wirings arearrayed at further outer side of said outermost detection wiring.
 5. Thetouch panel according to claim 2, wherein each of said plurality ofdetection wirings and said dummy wirings is made of a bundle of aplurality of metal thin lines.
 6. The touch panel according to claim 2,wherein each of said plurality of detection wirings and said dummywirings is formed of a transparent conductive material.
 7. The touchpanel according to claim 1, wherein said parasitic capacitance settingmeans is said outermost detection wiring, and a width of said outermostdetection wiring is formed smaller than those of other detectionwirings.
 8. The touch panel according to claim 1, comprising a pluralityof detection column wirings extended to a column direction and aplurality of detection row wirings extended to a row direction, as saidplurality of detection wirings.
 9. The touch panel according to claim 8,further comprising: a switch circuit that sequentially selects saidplurality of detection column wirings and said plurality of detectionrow wirings; an oscillation circuit that oscillates in a cyclecorresponding to a capacitance component of said detection wiringselected by said switch circuit; and a coordinate calculating circuitthat calculates coordinates of an indicator which touches said touchscreen, based on a change of an oscillation cycle of said oscillationcircuit.
 10. A display device comprising a display panel having saidtouch screen of the touch panel according to claim 9 arrayed on a frontsurface.
 11. The display device according to claim 10, wherein saidtouch screen of said touch panel is adhered to a front surface of saiddisplay panel.